Over 1.5 million Americans rely on manual wheelchairs for mobility, and over half report experiencing pain in their shoulders and/or other upper extremity (UE) joints. While there has been a great amount of research invested towards understanding the biomechanics of wheelchair propulsion, no definitive answers have been produced to determine the etiology of this pain. This may be due to the fact that laboratory collection of wheelchair propulsion may not fully represent real life conditions. To date, no data exists that compares laboratory versus field based measurements of wheelchair propulsion biomechanics. Additionally, currently available kinematic and kinetic data describing joint intersegmenal loads may not be adequate for explaining the loading on specific muscles and soft tissues. We propose to gain a deeper understanding of wheelchair propulsion by starting to obtain field-based data in combination with computer modeling. The first aim of this project is to contrast the forces and moments exerted during outdoor wheelchair propulsion using a pair of wireless instrumented wheels with data collected on a wheelchair ergometer during propulsion at the speed and power recorded during the outdoor trial. The second aim of the-study will involve the development of a musculoskeletal model to determine the activation patterns of the subjects as they propel on level ground, up a ramp, and along a sideslope. Optimization techniques will be used to determine muscle force distribution and model results will be validated through correlation with EMG data. Such a validated model will lend insight as to the changes in UE muscle response as users propel over varied terrains. It is our intent to provide a more realistic picture of UE intersegmental joint loads and muscle forces in the natural environment of the user. Subsequently this will aid in the development of therapeutic means to protect the shoulder from injury. [unreadable] [unreadable]